MVC ViewModel collections are null on postback - asp.net-mvc

Question

I have a view model which contains a class reference and 2 IEnumerable collections.
public class BuildingTypeViewModel
{
public Static_Item BuildingType { get; set; }
public IEnumerable<Reading_Type> ReadingTypes { get; set; }
public IEnumerable<Building_Type_Reading> BuildingReadings { get; set; }
}
I populate this ViewModel in the Edit action on the controller
public ActionResult Edit(int id)
{
Static_Item staticItem = db.Static_Item.Find(id);
BuildingTypeViewModel model = new BuildingTypeViewModel
{
BuildingType = staticItem,
ReadingTypes=db.Reading_Type.ToList(),
BuildingReadings = db.Building_Type_Reading.Where(bt => bt.UN_Building_Type == staticItem.UN_Building_Type).ToList()
};
return View(model);
}
Building type on the view model is a class with an ID and Description and the data would be something like this:
UN_Building_Type=1, Description = "Hospital"
The IEnumerable of Reading_Type's would be like this:
UN_Reading_Type = 1, Description = "Electric"
UN_Reading_Type = 2, Description = "Gas"
The IEnumerable of Building_Type_Readings would be like this:
UN_Building_Type_Readings=1, UN_Building_Type=1, UN_Reading_Type = 1, Typical=300, Good=150
UN_Building_Type_Readings=2, UN_Building_Type=1, UN_Reading_Type = 2, Typical=800, Good=400
I load this data into my view:
#model SSE.Enterprise.EE_Web_Portal.Models.BuildingTypeViewModel
#using (Html.BeginForm())
{
#Html.AntiForgeryToken()
<div class="form-horizontal">
<h4>Static_Item</h4>
<hr />
#Html.ValidationSummary(true, "", new { #class = "text-danger" })
#Html.HiddenFor(model => model.BuildingType.UN_Building_Type)
<div class="form-group">
#Html.LabelFor(model => model.BuildingType.Description, htmlAttributes: new { #class = "control-label col-md-2" })
<div class="col-md-10">
#Html.EditorFor(model => model.BuildingType.Description, new { htmlAttributes = new { #class = "form-control" } })
#Html.ValidationMessageFor(model => model.BuildingType.Description, "", new { #class = "text-danger" })
</div>
</div>
<div class="form-group">
<label class="control-label col-md-2">Building Readings</label>
<div class="col-md-10">
<table class="table">
<tr>
<th/>
<th>
#Html.LabelFor(model=>model.BuildingReadings.FirstOrDefault().Typical)
</th>
<th>
#Html.LabelFor(model => model.BuildingReadings.FirstOrDefault().Good)
</th>
</tr>
#foreach (var item in Model.ReadingTypes)
{
<tr>
<td>
#Html.Label(item.Description)
</td>
<td>
#Html.EditorFor(model => model.BuildingReadings.FirstOrDefault(b => b.UN_Reading_Type == item.UN_Reading_Type).Typical, new { htmlAttributes = new { #class = "form-control" } })
</td>
<td>
#Html.EditorFor(model => model.BuildingReadings.FirstOrDefault(b => b.UN_Reading_Type == item.UN_Reading_Type).Good, new { htmlAttributes = new { #class = "form-control" } })
</td>
</tr>
}
</table>
</div>
</div>
<div class="form-group">
<div class="col-md-offset-2 col-md-10">
<input type="submit" value="Save" class="btn btn-default" />
</div>
</div>
</div>
}
<div>
#Html.ActionLink("Back to List", "Index")
</div>
Here is my edit postback method.
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit([Bind(Include = "BuildingType")] BuildingTypeViewModel model)
{
if (ModelState.IsValid)
{
db.Entry(model).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
return View(model);
}
When the page is posted back the 2 IEnumerable collections are null so I'm not able to save the data that has been entered.
Any idea?
Ta

Answer 1

First of all, by specifying the attribute Bind(Include = "BuildingType") you're telling MVC to only bind this single property. Remove the attribute, and MVC will try to bind your 2 IEnumerable collections.
Next, check your #Html.EditorFor calls. I'm not sure MVC can understand FirstOrDefault inside. Try avoiding LINQ selectors inside your view.
And after that, as #will mentioned, try changing IEnumerable to List.